Release of the Narrow-Channel Lock in Porous Crystals for Direct Acetylene Purification

Acetylene (C₂H₂) is an essential chemical feedstock, yet removing carbon dioxide (CO₂) impurities in a single step remains a formidable challenge due to their nearly identical molecular sizes and boiling points. Here, we present that by releasing a "narrow-channel lock" through functional-group modulation, a porous crystal (NTU-87) overcomes this limitation. The parent framework NTU-87-NH₂ contains isolated nanopockets locked by -NH₂ groups, exhibiting negligible adsorption difference between CO₂ and C₂H₂ (2.9 cm³ g^-1 at 0.5 bar, 298 K). Removing these groups transforms the structure into NTU-87 with a ball-neck channel, markedly reversing the adsorption preference and amplifying the difference to 15.6 cm³ g^-1. Breakthrough experiments confirm that NTU-87 binds CO₂ more strongly than C₂H₂, enabling single-step production of pure C₂H₂ from CO₂/C₂H₂ mixtures with low regeneration energy. This strategy of unlocking confined pore architectures establishes functional-group regulation as a general route to high-performance gas purification.